The present invention relates to a multilevel interconnection structure for a semiconductor device and a method for forming the same.
One of the typical multilevel interconnections is illustrated in FIG. 1. Field oxide films 2 are selectively formed on a top surface of a silicon substrate 1 to define an active region of the substrate. A first inter-layer insulator 3 with a first contact hole is formed on the field oxide film 2 and the active region. A titanium film 5 is formed on the field oxide film 2 and on both a vertical side wall and a bottom of the first contact hole. A titanium nitride film 6 is formed on the titanium film 5. A tungsten plug is selectively provided within the first contact hole. An aluminum film 9 is formed on the titanium nitride film 6. A titanium nitride film 10 is formed on the aluminum film 9. A first interconnection layer 11 comprises the titanium film 5, the titanium nitride film 67 the aluminum film 9 and the titanium nitride film 10. A second inter-layer insulator 41 with a second contact hole over the first interconnection layer 11 is formed on the first interconnection layer 11 and on the first inter-layer insulator 3. A titanium film 15 is formed on the second inter-layer insulator 41 and on both a vertical side wall and a bottom of the second contact hole. A titanium nitride film 16 is formed on the titanium film 15. A tungsten plug 17 is selectively provided within the first contact hole. An aluminum film 18 is formed on the titanium nitride film 16. A titanium nitride film 19 is formed on the aluminum film 18. A second interconnection layer 20 comprises the titanium film 15, the titanium nitride film 16, the aluminum film 18 and the titanium nitride film 19. A third inter-layer insulator 42 is formed on the second interconnection layer 20 and on the second inter-layer insulator 41.
When electrical current flows through the aluminum interconnection, electromigration is likely to appear due to a small electromigration resistance of aluminum. Aluminum atoms are likely to migrate along the current of electrons. Electromigration may cause disconnection of the interconnection. Refractory metals have relatively high electromigration resistance. Refractory metal atoms decline to migrate, whilst aluminum atoms and non-refractory metal atoms incline to migrate. If electron current flows from the refractory metal region to aluminum region, then any void is likely to be formed in the aluminum region but in the vicinity of an interface to the refractory metal region. The formation of a void may lead to disconnection of the interconnection.
As illustrated in FIG. 2, a pair of low level interconnections 11 and 11a are arranged at a pitch P which is relatively large, for example, 1.6 micrometers. Another pair of high level interconnections 20 and 20a are connected to the low level interconnections via tungsten plugs within contact holes. When currents of electrons flow through the interconnections, tungsten atoms decline to migrate whilst aluminum atoms incline to migrate. For this reason, a hillock 44 and a void 43 are likely to be formed as illustrated in FIG. 3. If the pitch P is large, it is possible to provide pedestals 46 from which aluminum atoms are supplied to the void. However, the pitch has to be small when a high density integration is required. In this case, it is difficult to provide any pedestals.
In the above circumstance, it had been required to develop quite novel multilevel interconnection structures free from any problems with void and hillock.